It has, heretofore, been previously known that the natural, primary defense mechanisms against viral infection are mainly brought into play by the production of interferon although other hitherto unknown factors may also play a role and, therefore, cannot be excluded.
Interferon is a protein macro-molecule formed by the action of a virus and a host cell.
Interferon was discovered by A. Isaacs and J. Lindenmann, Proc. Roy. Soc. B 147,258 (1957) while studying virus interference. By producing interferon one virus can interfere with the growth of another virus added subsequently. The viruses need not be related and interference can be induced by inactivated as well as by live virus [G. Bodo, Naturwissenschaften 58 (1971) 425-429; J. L. Le Clero and J. Cogniaux--Le Clerc, Acta Virol. 9 (1965) 18-24; S. Hermodsson, Acta Path. Microbiol Scand. 62 (1964) 224-238; M. Harris, Science 170 (1970) 1068-1070)].
Interferons are generally believed to be proteins which cause a non-specific and non-immunological defense reaction against viral infections. Thus, for example, if a virus enters a host organism, the cells of the Recticulo-Endothial (R. E.) System, which constitute the major line of defense in the animal body, within a short time produce large quantities of interferon and produce a high interferon level in the circulatory system. This "circulating interferon" is rapidly distributed throughout the host organism and prevents the further spread of viral infection or of secondary infection.
As pointed out above, it has been established that the formation of interferon in a host organism can be stimulated by the therapeutic administration of both active and inactive viruses, however, a serious disadvantage of the therapeutic administration of such viruses is the simultaneous induction of virus-specific antibodies in the host organism which makes more difficult or prevents repeated administration of such viruses for stimulating the non-specific defense mechanisms because of the danger of allergization and/or anaphylactic shock within certain time intervals.
Additionally, there are many quite different microorganisms and substances which can cause formation of interferon by the host organism. Such microorganisms may be bacteria, endotoxins, phyto-haemaglutinins, natural and synthetic ribonucleic acids, such as, for example, polyinosinpolycytidylic acid (Poly I:C) as well as certain synthetic polymers possessing anionic character, for example, polyvinyl sulphate, polyacrylic acid and polymethacrylic acid as well as pyrane copolymers [Y.K.S. Murthy and H. P. Anders, Angew. Chem. internat. Edit. 9 (1970) 480-488]. However, these substances all suffer a serious disadvantage in that they are too toxic, for example, they cannot be physiologically degraded (as synthetic polymers) or that they show other strong side effects (as Poly I:C), so that they cannot be used clinically [Y.K.S. Murthy and H. P. Anders, Angew. Chem. internat. Edit. 9 (1970) 480-488; Nature 223 (1969) 715-718].